Foodstuffs such as fresh produce are subject to spoilage by the action of unwanted microbes such as molds and bacteria. Some examples of such produce are lemons, blueberries, kiwi fruit, apples, strawberries, nuts, and, grapes. Microbes are present on the produce prior to harvesting, and remain with produce as it moves from the field into processing facilities. In order to minimize damage to the harvested produce from the microbes, processors typically take steps that can include some or all of chemical fungicide treatment, liquid wash, and, cold storage for the produce. Each of these steps potentially provides potential remedial benefits, but each also has problematic aspects.
After harvesting, many produce types can be treated with chemical fungicides and/or bactericides in an attempt to inhibit microbe growth. Even after such treatment, microbe growth can cause damage, particularly as storage time is increased. Residual mold can continue to grow and can develop into large nesting molds. Fungicide treatment can be relatively expensive, due at least in part to the cost of the fungicides. Allergies to fungicides are common, and can adversely affect produce workers, other workers who have direct or indirect contact with the products, and eventual consumers of the products. Products treated with some chemical fungicides and/or bactericides are ineligible for designation and/or description as organic produce, and thus lose access to significant markets.
After harvesting, produce can be washed with a sanitizing liquid in order to remove dirt and other unwanted substances. The sanitizing liquid can be water mixed with various sanitizing agents. However, the shapes of many produce items contain crevices that are not effectively cleaned by this technique. Items can have irregular surfaces and numerous cavities and crevices. Surface tension of a sanitizing liquid such as water can prevent liquid from reaching into small cavities and crevices, thus adequate cleaning action cannot occur in those locations. Unwanted substances and microbes can remain undisturbed.
The reduced temperature environment of cold storage can inhibit microbial growth. However, cold storage is typically implemented at high humidity levels in order to prevent damaging the produce by dehydration. At typical high humidity cold storage levels such as 50% to 90% relative humidity, molds can be active. In such conditions, microbes such as molds can live, grow, and propagate, such as by sporulation. In order to maintain uniform temperature, air within cold storage units is typically continuously refrigerated and circulated, providing an ideal mechanism for spreading airborne spores throughout an entire refrigerated unit. The living and propagating microbes can significantly damage produce inventory within the storage unit.
In addition to molds, bacteria such as E Coli, Listeria and Salmonella can cause damage to fresh produce, and to dry products such as powders, flakes and seeds. Damage to fresh produce and dry products can take place in contained environments such as hoppers, silos, augers, pipelines, and various enclosures.
Thus what is needed are improved systems and methods for eliminating microbes on foodstuffs including fresh produce, stored fresh produce, and dry products, with particular attention to contained environments.
Attempts have been made to utilize ozone gas across a range of temperatures, such as −40 F to −100 F, as an anti-microbial agent. When the gas is taken directly from an ozone generator, it has little effect at reducing bacteria and mold spores. Typical ozone generators produce ozone gas at 0.2% to 10% ozone by weight, corresponding respectively to 2,000 to 100,000 ppm. The ozone gas produced is typically kept extremely dry (−40 to −100° F. dew point) in order to eliminate undesirable moisture in the ozone generating cell. Moisture passing through an ozone generating cell produces nitric acid that can cause severe damage to the cell and downstream equipment.
Many mold spores and spore forming microbes can tolerate high levels of dry ozone gas without being killed. However, water with ozone dissolved at levels between 0.2 and 10 ppm can be an effective killer of bacteria and mold spores that are planktonic, in very short times.
Thus what is needed are systems and methods increase the microbe-reducing effectiveness of ozone gas application to fresh produce, stored fresh produce, and dry products, with particular attention to contained environments.